1: This study evaluates the capabilities of near-infrared spectroscopy (NIRS) and electronic nose (E-nose) in characterizing fermented milk, focusing on the impact of feeding type and probiotic potential. Three separate trials were conducted to compare the effects of Total Mixed Ration (TMR) cow feeds enriched with polyunsaturated fatty acids against control feeds. Milk samples, collected from the feeding trials, were fermented with three Lactobacillus strains categorized based on their probiotic potential: moderate (M), non-probiotic (N), and probiotic (P). The probiotic (P) strain exhibited distinct biochemical changes that were easily identifiable by both technologies. The NIRS and E-nose datasets were analysed separately to highlight the individual strengths and unique contributions of each technique in discriminating sample attributes. Specific NIRS wavelengths (1600–1800 nm), associated with unsaturated fatty acids like oleic and linoleic acids, acted as reliable markers for distinguishing milk samples based on the feeding type, while the 1300–1600 nm range helped differentiate strains. E-nose analysis identified volatile compounds such as hexanal and 1-hexen-3-one, formed from the oxidative degradation of unsaturated fatty acids, highlighting the impact of bacterial strains and milk composition on aroma and flavor. The fatty acid profile, particularly the unsaturated fatty acids and their derivatives, played a crucial role in strain and diet selection, offering valuable insights into the development of fermented milk products with specific probiotic characteristics.

The utilization of corn silage in animal diets is becoming a challenge, due to the crop’s reduced yield as a result of climate change. Alternative silage types, such as mixtures of Italian ryegrass and winter cereals, may be a good complement to corn silage in diet formulation. Therefore, it is important to investigate how these alternative sources influence milk fatty acid and odor profile, as well as how these quality parameters could be efficiently evaluated. In this study, a corn silage-based control (CTR) and four experimental (EXP) diets—which contained winter cereals (WC), as well as WC with Italian ryegrass (IRG) silages in different proportions—were fed to Holstein-Friesian cows (n = 32) in a single-blinded efficacy study during a series of 4-week periods, with 2 weeks of adaption to each feed before the main trial. Milk from each trial was subjected to fatty acid (FA) analysis and odor profiling through the utilization of gas chromatography and an electronic nose, respectively. The results show that milk FAs in the EXP-3 and EXP-4 groups (which contained mixed silages using WC) changed the most when compared with other groups. Moreover, with a 7 kg/day inclusion rate of WC + IRG and of the WC silages in the diets of the EXP-2 and EXP-3 groups, respectively, the milk from these groups had their n6:n3 ratio reduced, thus indicating possible health benefits to consumers. The odor variation between the milk of the WC + IRG and WC groups was greater than the variation between the milk of the CTR and EXP groups. The main volatile compound responsible for the odor of the CTR milk was ethyl-butyrate, whereas 2-propanol and butan-2-one dominated the WC milk; the milk samples of the WC + IRG groups were influenced largely by ethanol. The study proved that with a 7 kg/day inclusion of mixed silages including winter cereals plus Italian ryegrass, the FA and odor profile of bovine milk could be modified.